Tobacco use is a major public health problem in the United States, with 47 million Americans smoking cigarettes. Over 400,00 lives are lost to tobacco related illness in the United States each year and cigarette smoking costs our economy over 50 million dollars in direct health care expenses annually. While many effective smoking cessation programs have been developed, these programs often have limited reach, thus decreasing their total impact on the population. We propose to develop an Internet-based smoking cessation program based on AHCPR guidelines and empirically validated treatment protocols. The innovative approach offered by this system provides a powerful tool for combining brief-counseling and self-change techniques with the most effective components of clinical interventions into a cost-effective and easily accessible package. This system will be marketed to HMOs and individual smokers. During Phase I we will develop and test a prototype of the eSTOP system and evaluate its usability through a within subject crossover design, as well as focus group research. In Phase 2 we plan to develop a final prototype and conduct a rigorous, controlled, experimental evaluation of eSTOP's clinical efficacy and cost effectiveness. PROPOSED COMMERCIAL APPLICATION: HMOs and other large-scale health care providers spend millions of dollars each year on smoking cessation interventions and the treatment of smoking-related illnesses. As a result, there is a great need for clinically efficacious, easily accessible, and cost-effective smoking cessation interventions. Capitalizing on the revolution in informatics and communications, we propose to develop and market a Web-based smoking cessation application that fulfills these needs.